In recent years, liquid crystal display devices using TFTs (Thin Film Transistors), as in notebook computers, cell phones, and liquid crystal televisions, have become widespread. In liquid crystal display devices using TFTs, a drive circuit called a “source driver” supplies voltage to a liquid crystal in order to control the state of display by the liquid crystal. The source driver is configured by a semiconductor such as an IC (Integrated Circuit). Semiconductors increase in cost as their withstanding voltage increases. Therefore, the cost of liquid crystal display devices is reduced by narrowing the amplitude of an output voltage from the source driver.
For example, Japanese Laid-Open Patent Publication Nos. 2002-202762, 2006-276879, and 2-157815 disclose inventions of methods for driving a liquid crystal display device in which “a voltage applied to a liquid crystal is greater than a voltage outputted from a source driver”. This will be described with reference to FIGS. 23 to 25. FIGS. 23A to 23C are diagrams describing operations in pixels of a liquid crystal display device in the conventional art. FIG. 24 is a block diagram illustrating an electrical configuration of the liquid crystal display device in the conventional art. FIG. 25 provides signal waveform diagrams describing Y-side operations in the conventional art.
In the conventional art, as shown in FIG. 23A, a TFT 116 is turned on first, and a voltage Vp is provided to a pixel electrode 118 from a source line 114. Then, as shown in FIG. 23B, the TFT 116 is turned off, and the voltage of an auxiliary capacitance line 113 changes by Vq. In this case, when it is assumed that an auxiliary capacitance 119 connected to the pixel electrode 118 has a capacity of Cstg, and a liquid crystal 105 has a capacity of Clc, the voltage Vr of the pixel electrode 118 is represented by equation (101) below:Vr=Vp+Vq×(Cstg/(Cstg+Clc))  (101), as shown in FIG. 23C.
Thus, the voltage applied to the pixel electrode 118 is set greater than the voltage Vp provided to the source line by Vq×(Cstg/(Cstg+Clc)). In this manner, the voltage provided to the source line can be set lower than a voltage to be applied to the pixel electrode, making it possible to narrow the amplitude of an output voltage from the source driver.
Note that in the conventional art, a voltage of each of auxiliary capacitance lines 113 should be controlled independently (for each of their corresponding gate lines 112). Therefore, as shown in FIG. 24, a flip-flop circuit 132 and a selector circuit (stored capacitance drive circuit) 134 are provided in each row for generating a voltage Yci to be provided to the auxiliary capacitance line 113 based on a signal Ysi provided to the gate line 112. Accordingly, by the flip-flop circuit 132 and the selector circuit 134, a signal Yci as shown in FIG. 25 is generated, and the voltage of the signal Yci is provided to the auxiliary capacitance line 113. In this case, the signal Yci is delayed by one horizontal scanning period from the signal Ysi provided to the gate line 112.
[Patent document 1] Japanese Laid-Open Patent Publication No. 2002-202762
[Patent document 2] Japanese Laid-Open Patent Publication No. 2006-276879
[Patent document 3] Japanese Laid-Open Patent Publication No. 2-157815